The FDA's Center for Drug Evaluation and Research recommends in a new guidance that developers of antiviral drugs and biological products conduct nonclinical studies on a range of subjects before starting a Phase I clinical trial.

These nonclinical studies can determine the investigational product's mechanism of action, help establish its specific antiviral activity in a model system and provide data on the development of viral resistance to it, among other things. Moreover, in cases where the product will be tested in a clinical trial in combination with other antiviral products, the developers should first conduct a nonclinical in vitro study in tandem with other approved products to determine whether the different products might interfere with each other.

The guidance is intended to help take developers of antiviral drugs and biological products from the initial pre-investigational new drug stage through the new drug application (NDA) or biologic license application and into the postmarketing stages. The document draws on studies that have been done on HIV-1 products "as a paradigm for studies of products to treat other viruses," inducing various principles that can be applied to products now being developed to treat other viral infections, such as hepatitis B, hepatitis C, herpes simplex, varicella zoster, influenza, rhinovirus, cytomegalovirus and human papillomavirus.

Companies may submit the completed reports on their nonclinical and clinical virology studies to the FDA as soon as they are done, instead of holding onto them until it is time to submit the NDA, the guidance states.

The full text of the guidance can be accessed at http://www.fda.gov/cder/guidance/7070fnl.htm (http://www.fda.gov/cder/guidance/7070fnl.htm).